Field of the Invention
The present invention relates to patch type antennas, and particularly but not exclusively to antennas suitable for use in portable radiotelephones.
Portable radiotelephones are presently becoming very widespread in numerous countries. One of the objects sought by the designers of such radiotelephones is to make them as small as possible so as to make them even more easy to use. One of the elements that gives rise to difficulties with such miniaturization is the antenna of the radiotelephone. In the vast majority of conventional radiotelephones, the antenna is external and therefore increases the overall size of the device.
Another problem associated with designing radio-telephones lies in the fact that two frequency bands are used at present for portable radiotelephone networks. Firstly there is the so-called "GSM" band which corresponds to frequencies in the range 890 MHz to 960 MHz, and secondly there is the so-called "DCS 1800" frequency band which extends from 1700 MHz to 1880 MHz.
It will therefore be advantageous to have radio-telephones capable of operating in either of those two frequency bands depending on the network being used.
It is relatively easy to provide electronic circuits in a radiotelephone that are capable of processing transmission and reception of signals corresponding to two different frequency bands, and typically those that are mentioned above. In contrast, designing an antenna that is suitable for two frequency bands constitutes a problem that is more difficult.
Patch type antennas have already been proposed for use in radiotelephones. Such an antenna can be placed inside the radiotelephone itself, thereby considerably reducing its overall size. Nevertheless, in that known solution, the patch antenna is suitable for operating in one frequency band only.
There thus exists a real need for an antenna of the patch type which is suitable in particular for portable telephones and which is capable of operating in two distinct frequency bands, and in particular in the above-mentioned frequency bands.